With exponential demand for wireless communications having high speed and large capacity, high-speed broadband wireless communication techniques have been required to meet such a demand and to process data at a high Gbps transfer rate. In recent developments, millimeter-wave band wireless communication modules having a wide bandwidth have drawn a lot of attention. One of the biggest issues regarding the high-speed broadband wireless communication techniques is to develop small size, low cost wireless communication modules operating at millimeter-wave bands, and this may be achieved in general through the use of a system-in-package (SiP) technique. In the SiP technique, an antenna is an absolute factor that determines the total size of a wireless communication module. However, when the antenna is installed at the same plane as a signal processing circuit, for example, a monolithic millimeter-wave integrated circuit (MMIC), the overall size of the wireless communication module increases and incomplete isolation between the antenna and the signal processing circuit is also likely to degrade the performance of the wireless communication module. As an attempt to resolve these problems, the antenna was attached to the rear side of the wireless communication module, so the wireless communication module was significantly reduced in size, thereby getting the benefits of low cost and small size.
Meanwhile, to reduce a loss between the antenna and the signal processing circuit, the wireless communication module includes a planar transmission line-to-waveguide transition apparatus that connects the antenna and MMIC, through a planar transmission line such as a microstrip line or a coplanar waveguide (CPW), to the waveguide.
For example, a conventional transition apparatus is described in the article by Yusuke Deguchi, Kunio Sakakibara, Nobuyoshi Kikuma and Hiroshi Hirayama, entitled “Millimeter-Wave Microstrip-to-Waveguide Transition Operating over Broad Frequency Bandwidth”, which is disclosed in IEEE MTT-S Int. Microwave Symp., pp. 2107-2110, June 2005.
The transition apparatus disclosed in the article by Yusuke Deguchi et al. exhibits low loss wide-band characteristics but has shortcomings in that an upper waveguide has to be manufactured additionally through a mechanical process and that the process of obtaining a certain shape of the upper waveguide is very difficult. This results in an increase in the overall size of the wireless communication module.
Another conventional transition apparatus is found in the article by Florian Poprawa, Andreas Ziroff, and Frank Ellinger, entitled “A Novel Approach for a Periodic Structure Shielded Microstrip Line to Rectangular Waveguide Transition”, which is disclosed in IEEE MTT-S Int. Microwave Symp., pp. 1599-1562, June 2007.
The transition apparatus disclosed in the article by Florian Poprawa et al. includes a periodic shield structure for shielding a microstrip line-waveguide transition. However, it requires an additional manufacturing process to attach the periodic shield structure to the microstrip line-waveguide transition part, which renders it difficult to make the wireless communication module small in size.
As described above, the conventional techniques require an additional waveguide structures i.e., an upper waveguide or a periodically structured shield, in addition to the existing waveguide, so as to transmit signals from the antenna that is attached to the rear side of the transition apparatus through the waveguide. Therefore, an additional process is needed for joining those structures with the wireless communication module. As a result, this makes the overall size of the wireless communication module bulky, and also makes the layout of the wireless communication module very complicated which incurs high manufacturing cost as well as brings about a difficulty for making the wireless communication module in small size.
Moreover, problems may occur by processing error during the manufacture of those structures, and the complexity of the matching circuit gets worse.
Therefore, there is a need for a transition apparatus which has a low insertion loss and a wide frequency band, but does not require an additional process in the wireless communication module operating at millimeter-wave bands, thereby realizing a low price transition apparatus of super-small size.